Many email messages, both within organizations and outside the firewall, are directed to a large amount of recipients. While in some cases, it is not very interesting for the recipient of an email message to be aware of other recipients of the message, in many other cases the recipient of the message is interested to know who else that he/she knows received the message. For example, a manager wants to see if any of his employees received the message; or a user wants to observe whether any of his close friends received the message as well.
For emails addressed to many recipients, the recipient list in the “To” and/or “Cc” header field gets harder to digest for the reader as those headers become larger. Thus, finding specific people on those lists becomes a time-consuming problem.